1. Field of the Invention
The present invention relates to network communication protocols and more particularly to a synchronous Ethernet capable of simultaneously providing a real-time service and a non-real-time service.
2. Description of the Related Art
Ethernet is the most widely used local area network technology and is now defined as a standard in an Institute of Electrical and Electronics Engineers (‘IEEE’) 802.3. However, Ethernet has been originally developed by Xerox and has been advanced by Xerox, Digital Equipment Corporation (DEC), Intel, and other similar companies.
In the conventional Ethernet, since a competitive access is accomplished by means of a carrier sense multiple access/collision detect (CSMA/CD) protocol stipulated in an IEEE 802.3, a service frame of an upper layer is converted to an Ethernet frame while an inter-frame gap (IFG) interval is maintained and the Ethernet frame is transmitted. Herein, a transmission is performed according to a generation sequence regardless of the kind of the upper service frames. That is, an Ethernet is a technology generally used when data are transmitted between different terminals or different users.
Such an Ethernet has not been known to be sufficient for transmitting a dynamic image and voice which are sensitive to a transmission time delay. However, recently, a technology has been discussed, which can transmit synchronous data such as image and voice by means of the existing Ethernet. Hereinafter, an Ethernet for transmission of data as described above will be called a “synchronous Ethernet.”
FIG. 1 is a view showing the transmission cycle of a synchronous Ethernet.
As shown in FIG. 1, in the synchronous Ethernet currently discussed, each of the transmission cycles n, 100 , and n+1, 200, for data transmission has one cycle of 125 μsec and includes a synchronous (sync) part 100-1 or 200-1 for transmission of synchronous data and an asynchronous (async) part 100-2 or 200-2 for transmission of asynchronous data.
Specifically, the sync part 100-1 or 200-1 for the transmission of the synchronous data is a data part having the highest priority in the transmission cycle. According to a proposal currently discussed, ten (10) sub-synchronous frames, each of which is constructed using 738 bytes, are contained in the sync part 100-1 or 200-1 as a default.
Further, the async part 100-2 or 200-2 for the transmission of the asynchronous data is constructed in a remainder portion of the frame excluding the sync part 100-1 or 200-1. Herein, variable asynchronous data are contained in a corresponding portion by the frame.
In the synchronous Ethernet currently discussed as described above, asynchronous data and synchronous data are contained in the conventional Ethernet frame and are then transmitted.
FIG. 2 is a view showing the structure of the conventional Ethernet frame.
As shown in FIG. 2, the conventional Ethernet frame includes a preamble field 21, a destination address (DA) field 22, a source address (SA) field 23, a length/type field 24, a data field 25 for indicating data of the frame, and a frame check sequence field (FCS) 26. The preamble field 21 is constructed using eight bytes and indicates the start and the end of the frame, the destination address field 22 is constructed using six bytes and indicates the media access control (‘MAC’) address of a destination to which the frame must be transmitted, and the source address field 23 is constructed using six bytes and indicates the MAC address of a station transmitting the frame. Further, the length/type field 24 is constructed using two bytes and indicates the length information of the data of the frame and the protocol type of the frame, and the frame check sequence (FCS) field 26 is constructed using four bytes and is disposed at the end of each frame. The FCS field is used for detecting an error when information is transmitted according to each frame in data communication.
When both synchronous data and asynchronous data are transmitted through the aforementioned structure of the conventional Ethernet frame, synchronization or non-synchronization may be confirmed through the length/type field 24.
A layer structure for processing the Ethernet frame as described above will be described with reference to FIG. 3.
FIG. 3 is a view showing the layer structure of an Ethernet network to which the present invention is applied.
The layer structure of the Ethernet network includes a physical (PHY) layer 34 which is a first layer of an OSI 7 stack, a MAC layer 32 which is the sub-layer of a data link layer and is a second layer of the OSI 7 layer stack, and MAC clients 31-1 to 31-3 which are upper layers of the stack. A Gbps (gigabit/second) media independent interface (‘GMII’) layer 33 is an interface layer between the PHY layer 34 and the MAC layer 32.
An operation of each layer will now be described. First, the PHY layer 34 includes a physical medium attachment (PMA), a physical medium dependent (PMD), and a physical coding sub-layer (PCS) and transmits inputted Ethernet data to the upper MAC layer 32. The MAC layer 32 confirms or determines information, such as the destination address and the length/type, from the transmitted Ethernet data and transmits the information to the corresponding MAC client 31-1, 31-2 or 31-3. These operations are well-known in the art and need not be discussed or shown in detail herein.
A description when the synchronous Ethernet, as described in FIG. 1, is applied to the aforementioned layer structure is as follows. First, a maximum of 16 synchronous Ethernet frames having a fixed length and including a maximum of 192 slots, each of which is constructed using four bytes, are transmitted in a transmission interval for synchronous data in the synchronous Ethernet. When the transmission of such synchronous frames is completed in one cycle, asynchronous frames are transmitted during the remaining interval of the corresponding cycle. In such a superframe scheme, in the case of the conventional synchronous Ethernet, a synchronous frame and an asynchronous frame are distinguished from each other through the length/type field 24 contained in an overhead. Accordingly, synchronous data and asynchronous data are distinguished from each other and processed in the MAC layer 32.
However, when such a general network layer structure is employed, a processing is performed even for synchronous data through the destination address information and the length/type information. Therefore, unnecessary overhead is added, thereby reducing the transmission efficiency. That is, since the synchronous data are data containing, for example, video or audio broadcasting information and transmitted in a broadcasting scheme, and each device approves or excludes corresponding data, it is unnecessary to transmit the data through an address processing, etc., in the MAC layer.
Accordingly, it is necessary to prevent unnecessary overhead from being added by distinguishing and processing synchronous data and asynchronous data in the PHY layer 34. Further, it is necessary to carry out research on a data processing scheme enabling various types of synchronous data to be transmitted according to each type of the synchronous data.